1. Field of the Invention
The present invention relates to a self displacement sensing cantilever for a scanning probe microscope for measuring a surface shape or analyzing physical properties of a surface of a sample by bringing a cantilever having a probe at its tip close to or into contact with the sample. The present invention also relates to a scanning probe microscope having the self displacement sensing cantilever.
2. Description of the Related Art
There is known a scanning probe microscope as an apparatus for measuring a very small region of a sample such as a metal, a semiconductor, a ceramic, a resin, a high polymer, a biomaterial, an insulator, or the like, so as to measure a shape or physical property information such as electric, magnetic, optical, or mechanical characteristic, and the like of a surface of the sample.
In such scanning probe microscope, a cantilever having a probe at its tip is brought close to or into contact with the sample surface, and the sample is relatively scanned by the probe with a triaxial micromotion mechanism in a sample plane (XY direction). During this scanning action, a displacement amount of the cantilever is measured by a displacement detection mechanism while the sample or the probe is moved in the direction (Z direction) perpendicular to the sample surface for controlling a distance between the sample and the probe, and hence the surface shape and various types of physical property information are measured.
Here, as a usual displacement detection mechanism of the cantilever, a laser is projected to a back surface of the cantilever, and reflection light from the cantilever is detected by a photodetector so that a displacement amount is detected from a spot position on the photodetector. This displacement detection mechanism is called an “optical leverage system”. However, the displacement detection mechanism according to the optical leverage system requires adjustment of optical axis for projecting the laser beam to the back surface of the cantilever and receiving the reflection light from the cantilever in a detection surface of the photodetector before the measurement, and the adjustment work takes long time and much effort. In addition, when the scanning probe microscope is used, an optical microscope is usually disposed above or below the sample, and hence the sample and the probe are observed simultaneously by the optical microscope for positioning of a part of the sample to be measured with the probe tip based on an image on the optical microscope. However, the displacement detection mechanism of the optical leverage system is interposed between an objective lens of the optical microscope and the sample or the cantilever, and hence the working distance is short and an objective lens having a large numerical aperture may not be used. As a result, high resolution observation may not be performed with the optical microscope.
In addition, also in a case of a scanning near-field microscope for measuring optical characteristics of the sample surface with a scanning probe microscope, an objective lens is used for a purpose of condensing light from a light source so as to excite an evanescent field on the sample surface or condensing light generated by interaction between the probe tip and the sample. However, there is the case where an objective lens having a large numerical aperture may not be used because of the interposition of the displacement detection mechanism, which causes deterioration of the exciting efficiency or the condensing efficiency, or light of the optical leverage is mixed with detection light for the optical characteristic, which causes an increase of noise or a lowered resolution and hence disturbs accurate measurement.
In order to solve the above-mentioned problem due to the optical leverage system, a self displacement sensing cantilever is available for actual use in which the cantilever itself is equipped with a displacement detecting portion for detecting a displacement of the cantilever.
Here, with reference to Japanese Patent Application Laid-open No. 05-248810, a structure of a conventional self displacement sensing cantilever is described.
As illustrated in FIGS. 9A to 9C, the conventional self displacement sensing cantilever has a cantilever portion 112 constituted of two beams 112a and 112b protruding from a proximal end portion 116. The two beams 112a and 112b are combined at the tip to make a triangular free end, which is provided with a probe 114 having a sharp-pointed tip. The cantilever portion 112 is constituted of a lamination of a silicon layer 120, a piezoresistance layer 122, and an insulation layer 124. Among the layers, the piezoresistance layer functions as a displacement detecting portion and is formed by implanting boron into the surface of the silicon layer constituting the cantilever portion. In addition, the insulation layer is formed by depositing silicon oxide. Further, the proximal end portion of the cantilever portion 112 is provided with electrodes 118 that are electrically connected to the piezoresistance layer 122 via contact holes 126.
The self displacement sensing cantilever having such structure is connected to a displacement measurement circuit disposed externally via the electrodes 118. The displacement measurement circuit includes a voltage applying circuit and a current detecting circuit, so as to apply a predetermined DC voltage to the piezoresistance layer. Current flowing in this case is always measured by the current detecting circuit inside the displacement measurement circuit 140. If a displacement occurs in the cantilever portion, the displacement causes a change of specific resistance of the piezoresistance layer 122 so that current flowing in the piezoresistance layer 122 changes. Therefore, the displacement of the cantilever portion 112 may be measured by detecting the change of current value by the current detecting circuit inside the displacement measurement circuit.
It is noted that there is a type of the self displacement sensing cantilever having no insulation layer.
However, the conventional self displacement sensing cantilever has a problem as described below.
Because the cantilever portion is made of a semiconductor, photocurrent is generated when the cantilever portion is irradiated with light. Therefore, current having no relationship with a displacement of the cantilever portion may flow in the current detecting circuit, and hence a malfunction may occur in the displacement detecting circuit due to optical noise, or a noise component in the measurement data may increase.
Therefore, it is impossible to perform the measurement with the scanning probe microscope at the same time as projecting light to the cantilever, and it is necessary to perform the projection of light and the measurement with the scanning probe microscope alternately.
Therefore, observation with the optical microscope may not be performed in the state where the sample is close to the probe, and hence accuracy of positioning of the part to be measured by the image of the optical microscope is deteriorated.
In addition, in the case of the scanning near-field microscope that requires to project exciting light in the state where the probe and the sample are close to each other, the exciting light causes optical noise to render distance control impossible.
In addition, if the scanning probe microscope is used for measuring electric characteristics or magnetic characteristics, or measuring optical characteristics by dispersing the near field generated on the sample surface by the probe tip, it is necessary to form a functional coating for enhancing conductivity, magnetic property, or light amplifying effect on the cantilever portion including the probe tip. Such functional coating usually has conductivity of metal or the like. Therefore, if the coating is formed directly on the displacement detecting portion or the electrode portion of the cantilever, the electrode portion or the piezoresistance member may be short-circuited so that the displacement detecting portion does not work. Therefore, it is necessary to form the functional coating while protecting the electrode portion or the piezoresistance member portion, which takes a long manufacturing time period and much cost due to complicated film forming steps.